Is my frankenmotor dying?

[the_wizard_of_fire]

ive got a 91 eliminator with an odd engine issue....

 

when i go uphill, or get on the freeway, i get a really bad shudder from the engine on acceleration. it only lasts while i have the throttle about halfway, if i let up, or floor it, it stops. also I'm 90% sure its not a tranny or DW issue, because ive gotten it to shudder like this idling in park. WTF could cause this.

 

also, i refer to it as a frankenmotor, because i THINK its a renix block, with 91' chrystler everything else, as when i biught it, P.O. told me the engine was from an 86'? cherokee, but in being here, ive learned that motor would have been an AMC Renix, yet it has chrystler fuel injection, but the oil filter for the chrystler-produced engines doesnt fit, and i have to go back in years till it changes. so i guess the second part of this post is; WTF did the P.O. do? :huh???:

[500 MJ]

Is it a 4 cyl or 6 cyl?

[shelbyluvv]

Is it a 4 cyl or 6 cyl?

 

Should be a 4.0 considering it is a Eliminator.

 

If I had to guess it would put my money on either the o2 sensor, TPS, MAP, or a vacuum leak.

 

Is the truck giving you any codes or a CEL?

[dasbulliwagen]

4.0 wasnt produced for the 86 model year. I hope someone didnt swap in a 2.8 V6 drivetrain! We need more details about your truck, engine, trans, 2 0r 4 wheel drive.... all that stuff.

[Squeegy410]

and is it automatic or stick? Because it sounds like a passing gear linkage problem even though you said it wasn't the transmission. Passing gear linkage is more relative to fuel anyway. Sence when you floor it it stops shuttering it sounds like its shifting up when it doesn't need to and shifting down to the right gear when you give it gas. And it doing it sitting still may not be realated because my jeep (a stick shift) shutters sitting still sometimes but when I'm on the road it only shutters when I shift too soon. Thats my take on it but I could really use some more info about the truck.

[the_wizard_of_fire]

4.0 six, 4X4, full guages, with an auto tranny.

 

Squeegy: it acts like the same shudder, and what i diddnt say was that its not just rough idle (though my idle IS pretty crappy) its when i rev the engine when its in park.

 

Shelby: no codes at all, at least no dash lights. i don't have access to a code reader to see if its got one, and just isnt telling me...

 

Dasbull: I'm not at all positive what the block is out of. i know he said it was a cherokee, and the 91' 4.0 oil filter does not fit.

[TrailReadyMJ]

I had the same shudder you are describing, a couple different times, with a couple different issues.

 

The "shudder" you are feeling is probably a miss in the motor. When I first picked my MJ up, it would start and idle smooth as can be. However once you hit the gas it would shudder, especially when there was a load on it, but it did so this in park.

 

I brought her home, changed the plugs, wires and distributor cap, (they were ridiculously bad!) and it solved the problem... at least for a while.

 

Then last summer, it started acting up again, and only got worse over time. Turns out this time the problem was a little deeper, and was caused by a worn/loose timing chain. That motor was old and tired, and I already had a HO motor from my old XJ, so I just swapped it in as I had originally planned to do anyway.

 

Another similar experience I've had was back when I got my first XJ. It had a weird shudder, but it was primarily when engaged in reverse. It didn't act up at all in park though. This turned out to be caused by the fact 3 out of the 4 bolts were MISSING that mounted the bellhousing to the motor! The one that was left was backed out about 1/4" or so! At least I managed to catch this before it did any real damage! I replaced and torqued the bolts and it ran like new!

 

You just gotta love the little things prior owners of vehicles leave you with!

[AmJay]

One possibility is that it isn't the engine at all. The only time I've had a shudder when accelerating was after changing tires. They forgot to tighten the lug nuts and it was tire shake.. I thought the engine was coming apart.

 

Mac...

[the_wizard_of_fire]

I had the same shudder you are describing, a couple different times, with a couple different issues.

 

The "shudder" you are feeling is probably a miss in the motor. When I first picked my MJ up, it would start and idle smooth as can be. However once you hit the gas it would shudder, especially when there was a load on it, but it did so this in park.

 

I brought her home, changed the plugs, wires and distributor cap, (they were ridiculously bad!) and it solved the problem... at least for a while.

 

Then last summer, it started acting up again, and only got worse over time. Turns out this time the problem was a little deeper, and was caused by a worn/loose timing chain. That motor was old and tired, and I already had a HO motor from my old XJ, so I just swapped it in as I had originally planned to do anyway.

 

Another similar experience I've had was back when I got my first XJ. It had a weird shudder, but it was primarily when engaged in reverse. It didn't act up at all in park though. This turned out to be caused by the fact 3 out of the 4 bolts were MISSING that mounted the bellhousing to the motor! The one that was left was backed out about 1/4" or so! At least I managed to catch this before it did any real damage! I replaced and torqued the bolts and it ran like new!

 

You just gotta love the little things prior owners of vehicles leave you with!

 

ug, i so do not want it to be the timing chain.... :wall:

[Squeegy410]

I had the same shudder you are describing, a couple different times, with a couple different issues.

 

The "shudder" you are feeling is probably a miss in the motor. When I first picked my MJ up, it would start and idle smooth as can be. However once you hit the gas it would shudder, especially when there was a load on it, but it did so this in park.

 

I brought her home, changed the plugs, wires and distributor cap, (they were ridiculously bad!) and it solved the problem... at least for a while.

 

Then last summer, it started acting up again, and only got worse over time. Turns out this time the problem was a little deeper, and was caused by a worn/loose timing chain. That motor was old and tired, and I already had a HO motor from my old XJ, so I just swapped it in as I had originally planned to do anyway.

 

Another similar experience I've had was back when I got my first XJ. It had a weird shudder, but it was primarily when engaged in reverse. It didn't act up at all in park though. This turned out to be caused by the fact 3 out of the 4 bolts were MISSING that mounted the bellhousing to the motor! The one that was left was backed out about 1/4" or so! At least I managed to catch this before it did any real damage! I replaced and torqued the bolts and it ran like new!

 

You just gotta love the little things prior owners of vehicles leave you with!

 

ug, i so do not want it to be the timing chain.... :wall:

 

atleast if it is you know what it is. :D